Potsdam (dpa) – Heat alarm in southern Europe, floods in the USA, heavy rains in Japan – this summer people in many regions of the world are struggling with extreme weather and their consequences. According to studies, such events are becoming more frequent, which does not surprise scientists.
“For decades, climate researchers have been warning of increasing heat, drought and the resulting fires, as well as heavy rain and the resulting floods as a result of global warming caused by greenhouse gas emissions,” says Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research (PIK). “The predictions have been coming in for many years, as the measurement data show.”
Rahmstorf explains that extreme weather conditions have been steadily increasing for decades. This trend could continue. “The same extremes that have been increasing for decades will continue to increase until the world has achieved carbon neutrality.” In the future, events could even occur that have never happened in the recent past.
Many phenomena are already easy to explain: “Higher temperatures lead to increased drought because the soil and vegetation dry out more quickly due to the greater evaporation if it doesn’t rain a lot,” explains Rahmstorf. But not only drought is a consequence of the heat. “Higher temperatures also lead to more extreme precipitation because warm air can absorb more water vapor and then rain down.” According to a study in the journal Climate and Atmospheric Science, the number of precipitation records has risen sharply. On average, one in four record high daily precipitation events can be attributed to climate change.
Fast action required
The meteorological summer already set many records this year: according to the EU climate change service Copernicus, June has never been as warm as this year since records began. According to the local authorities, Canada is suffering from the worst forest fire season in its history. And the average global temperature for several days in July was above the previous record set in 2016, according to Climate Reanalyzer data from the American University of Maine.
From Rahmstorf’s point of view, it is important to act – and quickly. It is important to avoid the unmanageable through rapid climate protection and at the same time to adapt as well as possible to the unavoidable part of climate change, he explains. In the Paris Agreement, the states had agreed to limit global warming to 1.5 degrees if possible. But Rahmstorf fears that this goal will be missed. “As long as the use of fossil energy is still subsidized, self-imposed climate targets, for example in the transport sector, are ignored and immediately effective free measures such as a general speed limit are not used, there can be no question of serious efforts towards 1.5 degrees.”
Is climate change affecting the jet stream?
Europe is more than other mid-latitude regions affected by increasing heat. “This is attributed to more frequent and prolonged occurrences of a double jet stream weather pattern, as is currently the case again,” explains Rahmstorf.
The jet stream is a ribbon-like field of strong winds at an altitude of about ten kilometers that winds around the earth over the northern latitudes. A double jet stream splits into two branches. As a result, the jet stream layers last longer and, according to a study by PIK, cause more frequent heat waves in Western Europe.
The wavy jet stream can also form large bulges worldwide. If these remain over a region and do not move further around the earth, then unfavorable weather conditions can also settle there for a long time. The climate researcher Kai Kornhuber from the think tank Climate Analytics and the German Society for Foreign Relations said that it is currently being discussed to what extent climate change is contributing to the amplification of this phenomenon.
Long periods of heat possible
What is certain is that the Arctic is currently warming up faster than the regions on the equator, so the temperature difference is becoming smaller. However, this difference is a main driver of large-scale winds, explained Kornhuber. Therefore, its reduction may be an additional reason why the atmospheric circulation in the mid-latitudes slows down and extreme weather events last longer in a region.
All in all, it looks as if the weather patterns are also becoming more regionally persistent? For example, a heat wave lasts longer, says Kornhuber. Particularly in regions of extreme aridity, interactions between heat and drought could further intensify. “However, the undisputed main reason for the increased occurrence of heat waves is the warming of the atmosphere due to the increased concentration of greenhouse gases,” emphasized Kornhuber.
According to the latest data from the World Weather Organization (WMO), the concentrations of the greenhouse gases carbon dioxide, methane and nitrous oxide in the atmosphere reached new highs in 2021. There is concern that ecosystems on land and the oceans can absorb less and less CO2. So far, they buffer some CO2. In some land regions of the world, the transition from CO2 sink to source is already underway, for example in parts of the Amazon rainforest.
Climate researchers: Other factors besides global warming
Temperatures in the oceans are also showing extreme values this summer. In general, this is also due to the “increase in greenhouse gases in our atmosphere,” says Rahmstorf. Because of the heat storage capacity of the water, a little more than 90 percent of the additional energy captured went into the ocean. “Therefore, there have been regular new heat records there for decades.”
According to the “Climate Reanalyzer” data, the average surface temperature of the seas has been at a record high since March: every single day is the warmest for its respective date. Measurements started 40 years ago. In the past few days, the temperature has been around 0.8 degrees higher than the average for the same period from 1982 to 2011.
Rahmstorf assumes that several other factors contribute to the increase in addition to global warming. This also includes the El Niño event, which causes surface temperatures to rise in the tropical Pacific. El Niño is a natural phenomenon that occurs every few years. It can exacerbate the consequences of climate change because it has an additional warming effect. Depending on the region of the world, El Niño causes more heat and droughts or more floods.
2023-07-23 11:16:03
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